Effects of the BDNF val66met polymorphism on prefrontal brain function in a population at high genetic risk of schizophrenia

Increased serum brain-derived neurotrophic factor levels following electroconvulsive therapy or antipsychotic treatment in patients with schizophrenia

BACKGROUND

Many schizophrenia patients experience residual symptoms even after treatment. Electroconvulsive therapy (ECT) is often used in medication-resistant schizophrenia patients when pharmacologic interventions have failed; however, the mechanism of action is unclear. Brain-derived neurotrophic factor (BDNF) levels are reduced in drug-naive, first-episode schizophrenia and are increased by antipsychotic treatment. We tested the hypothesis that ECT increases serum BDNF levels by measuring BDNF concentrations in schizophrenia patients before and after they received ECT.

METHODS

A total of 160 patients with schizophrenia were examined. The ECT group (n=80) was treated with antipsychotics and ECT (eight to 10 sessions administered every other day). The drug therapy group (n=80) received only antipsychotic treatment. A control group (n=77) was recruited that served as the baseline for comparison.

RESULTS

Baseline serum BDNF level in ECT group was lower than in controls (9.7±2.1 vs. 12.4±3.2ng/ml; P<0.001), but increased after ECT, such that there was no difference between the two groups (11.9±3.3 vs. 12.4±3.2ng/ml; P=0.362). There was no correlation between patients' Positive and Negative Syndrome Scale (PANSS) score and serum BDNF level before ECT; however, a negative correlation was observed after ECT (total: r=-0.692; P<0.01). From baseline to remission after ECT, serum BDNF level increased (P<0.001) and their PANSS score decreased (P<0.001). Changes in BDNF level (2.21±4.10ng/ml) and PANSS score (28.69±14.96) were positively correlated in the ECT group (r=0.630; P<0.01).

CONCLUSIONS

BDNF level was lower in schizophrenia patients relative to healthy controls before ECT and medication. BDNF level increased after ECT and medication, and its longitudinal change was associated with changes in patients' psychotic symptoms. These results indicate that BDNF mediates the antipsychotic effects of ECT.

BDNF rs6265 methylation and genotype interact on risk for schizophrenia

Epigenetic mechanisms can mediate gene-environment interactions relevant for complex disorders. The BDNF gene is crucial for development and brain plasticity, is sensitive to environmental stressors, such as hypoxia, and harbors the functional SNP rs6265 (Val(66)Met), which creates or abolishes a CpG dinucleotide for DNA methylation. We found that methylation at the BDNF rs6265 Val allele in peripheral blood of healthy subjects is associated with hypoxia-related early life events (hOCs) and intermediate phenotypes for schizophrenia in a distinctive manner, depending on rs6265 genotype: in ValVal individuals increased methylation is associated with exposure to hOCs and impaired working memory (WM) accuracy, while the opposite is true for ValMet subjects. Also, rs6265 methylation and hOCs interact in modulating WM-related prefrontal activity, another intermediate phenotype for schizophrenia, with an analogous opposite direction in the 2 genotypes. Consistently, rs6265 methylation has a different association with schizophrenia risk in ValVals and ValMets. The relationships of methylation with BDNF levels and of genotype with BHLHB2 binding likely contribute to these opposite effects of methylation. We conclude that BDNF rs6265 methylation interacts with genotype to bridge early environmental exposures to adult phenotypes, relevant for schizophrenia. The study of epigenetic changes in regions containing genetic variation relevant for human diseases may have beneficial implications for the understanding of how genes are actually translated into phenotypes.

Serum brain-derived neurotrophic factor levels and psychotic symptoms in heroin dependence

OBJECTIVES

Psychotic symptoms are commonly observed among heroin users. Low serum brain-derived neurotrophic factor (BDNF) levels have been reported in schizophrenia and psychosis; however, studies assessing the relationship between serum BDNF levels and psychotic symptoms in heroin dependence are lacking.

METHOD

A total of 31 heroin-dependent patients who had never experienced psychotic symptoms during heroin consumption and 21 patients with a history of psychotic symptoms were consecutively recruited. We measured by enzyme-linked immunosorbent assay (ELISA) serum BDNF levels during early abstinence. A gender- and age-matched sample of healthy controls was also recruited and underwent measurement of BDNF.

RESULTS

BDNF levels were significantly lower in patients with psychotic symptoms than in those without psychotic symptoms (P<0.001). BDNF levels were not found to be correlated with sex, age, age of onset, duration of heroin use, average daily dose of heroin use, frequency of heroin use, SDS scores, BAI scores and BDI scores in the psychotic subsamples (all P>0.05).

CONCLUSIONS

Our findings suggest that heroin-dependent patients with psychotic symptoms share some of the neurotrophic insult that characterizes schizophrenia and psychosis.

The BDNF gene Val66Met polymorphism as a modifier of psychiatric disorder susceptibility: progress and controversy

Brain-derived neurotrophic factor (BDNF) has a primary role in neuronal development, differentiation and plasticity in both the developing and adult brain. A single-nucleotide polymorphism in the proregion of BDNF, termed the Val66Met polymorphism, results in deficient subcellular translocation and activity-dependent secretion of BDNF, and has been associated with impaired neurocognitive function in healthy adults and in the incidence and clinical features of several psychiatric disorders. Research investigating the Val66Met polymorphism has increased markedly in the past decade, and a gap in integration exists between and within academic subfields interested in the effects of this variant. Here we comprehensively review the role and relevance of the Val66Met polymorphism in psychiatric disorders, with emphasis on suicidal behavior and anxiety, eating, mood and psychotic disorders. The cognitive and molecular neuroscience of the Val66Met polymorphism is also concisely reviewed to illustrate the effects of this genetic variant in healthy controls, and is complemented by a commentary on the behavioral neuroscience of BDNF and the Val66Met polymorphism where relevant to specific disorders. Lastly, a number of controversies and unresolved issues, including small effect sizes, sampling of allele inheritance but not genotype and putative ethnicity-specific effects of the Val66Met polymorphism, are also discussed to direct future research.

Dysplasticity, metaplasticity, and schizophrenia: Implications for risk, illness, and novel interventions

In this paper, we review the history of the concept of neuroplasticity as it relates to the understanding of neuropsychiatric disorders, using schizophrenia as a case in point. We briefly review the myriad meanings of the term neuroplasticity, and its neuroscientific basis. We then review the evidence for aberrant neuroplasticity and metaplasticity associated with schizophrenia as well as the risk for developing this illness, and discuss the implications of such understanding for prevention and therapeutic interventions. We argue that the failure and/or altered timing of plasticity of critical brain circuits might underlie cognitive and deficit symptoms, and may also lead to aberrant plastic reorganization in other circuits, leading to affective dysregulation and eventually psychosis. This "dysplastic" model of schizophrenia can suggest testable etiology and treatment-relevant questions for the future.

BDNF val66met genotype and schizotypal personality traits interact to influence probabilistic association learning

The brain derived neurotrophic factor (BDNF) val66met polymorphism rs6265 influences learning and may represent a risk factor for schizophrenia. Healthy people with high schizotypal personality traits display cognitive deficits that are similar to but not as severe as those observed in schizophrenia and they can be studied without confounds of antipsychotics or chronic illness. How genetic variation in BDNF may impact learning in individuals falling along the schizophrenia spectrum is unknown. We predicted that schizotypal personality traits would influence learning and that schizotypal personality-based differences in learning would vary depending on the BDNF val66met genotype. Eighty-nine healthy adults completed the Schizotypal Personality Questionnaire (SPQ) and a probabilistic association learning test. Blood samples were genotyped for the BDNF val66met polymorphism. An ANOVA was performed with BDNF genotype (val homozygotes and met-carriers) and SPQ score (high/low) as grouping variables and probabilistic association learning as the dependent variable. Participants with low SPQ scores (fewer schizotypal personality traits) showed significantly better learning than those with high SPQ scores. BDNF met-carriers displaying few schizotypal personality traits performed best, whereas BDNF met-carriers displaying high schizotypal personality traits performed worst. Thus, the BDNF val66met polymorphism appears to influence probabilistic association learning differently depending on the extent of schizotypal personality traits displayed.

Translational findings on brain-derived neurotrophic factor and anxiety: contributions from basic research to clinical practice

BACKGROUND/AIMS

Anxious responses are evolutionarily adaptive, but excessive fear can become disabling and lead to anxiety disorders. Translational models of anxiety might be useful sources for understanding the neurobiology of fear and anxiety and can contribute to future proposals of therapeutic intervention for the disorders studied. Brain-derived neurotrophic factor (BDNF), which is known for its importance on neuroplasticity and contextual memory, has emerged as a relevant element for emotional memory. Recent studies show that the Val(66)Met BDNF polymorphism correlates with various psychiatric disorders, including anxiety, but there are several differences between experimental and clinical studies.

METHODS

In this work, we review the literature focused on the BDNF Val(66)Met polymorphism and anxiety, and discuss biological findings from animal models to clinical studies.

RESULTS

As occurs with other psychiatric disorders, anxiety correlates with anatomical, behavioral and physiological changes related to the BDNF polymorphism. In animal studies, it has been shown that a significant decrease in regulated secretion from both BDNFVal/Met and BDNFMet/Met neurons represented a significant decrease in available BDNF.

CONCLUSION

These studies suggest that developing pharmacological strategies facilitating the release of BDNF from synapses or prolongation of the half-life of secreted BDNF may improve the therapeutic responses of humans expressing the BDNF polymorphism.

The BDNF Val66Met polymorphism and plasma brain-derived neurotrophic factor levels in Han Chinese patients with bipolar disorder and schizophrenia

OBJECTIVE

Brain-derived neurotropic factor (BDNF) is widely distributed in the peripheral and central nervous systems. BDNF and its gene polymorphism may be important in synaptic plasticity and neuron survival, and may become a key target in the physiopathology of several mental illnesses. To elucidate the role of BDNF, we compared the plasma BDNF levels and the BDNF Val66Met gene variants effect in several mental disorders.

METHOD

We enrolled 644 participants: 177 patients with bipolar I disorder (BP-I), 190 with bipolar II disorder (BP-II), 151 with schizophrenia, and 126 healthy controls. Their plasma BDNF levels and BDNF Val66Met single nucleotide polymorphisms (SNP) were checked before pharmacological treatment.

RESULTS

Plasma levels of BDNF were significantly lower in patients with schizophrenia than in healthy controls and patients with bipolar disorder (F = 37.667, p<0.001); the distribution of the BDNF Val66Met SNP was not different between groups (χ(2) = 5.289, p = 0.507). Nor were plasma BDNF levels significantly different between Met/Met, Met/Val, and Val/Val carriers in each group, which indicated that the BDNF Val66Met SNP did not influence plasma BDNF levels in our participants. Plasma BDNF levels were, however, significantly negatively correlated with depression scores in patients with bipolar disorder and with negative symptoms in patients with schizophrenia.

CONCLUSION

We conclude that plasma BDNF profiles in different mental disorders are not affected by BDNF Val66Met gene variants, but by the process and progression of the illness itself.

A review of neuroimaging studies of young relatives of individuals with schizophrenia: a developmental perspective from schizotaxia to schizophrenia

In an effort to identify the developing abnormalities preceding psychosis, Dr. Ming T. Tsuang and colleagues at Harvard expanded Meehl's concept of "schizotaxia," and examined brain structure and function in families affected by schizophrenia (SZ). Here, we systematically review genetic (familial) high-risk (HR) studies of SZ using magnetic resonance imaging (MRI), examine how findings inform models of SZ etiology, and suggest directions for future research. Neuroimaging studies of youth at HR for SZ through the age of 30 were identified through a MEDLINE (PubMed) search. There is substantial evidence of gray matter volume abnormalities in youth at HR compared to controls, with an accelerated volume reduction over time in association with symptoms and cognitive deficits. In structural neuroimaging studies, prefrontal cortex (PFC) alterations were the most consistently reported finding in HR. There was also consistent evidence of smaller hippocampal volume. In functional studies, hyperactivity of the right PFC during performance of diverse tasks with common executive demands was consistently reported. The only longitudinal fMRI study to date revealed increasing left middle temporal activity in association with the emergence of psychotic symptoms. There was preliminary evidence of cerebellar and default mode network alterations in association with symptoms. Brain abnormalities in structure, function and neurochemistry are observed in the premorbid period in youth at HR for SZ. Future research should focus on the genetic and environmental contributions to these alterations, determine how early they emerge, and determine whether they can be partially or fully remediated by innovative treatments.

BDNF serum concentrations in first psychotic episode drug-naïve schizophrenic patients: associations with personality and BDNF Val66Met polymorphism

AIMS

To investigate the relationship among brain derived neurotrophic factor (BDNF) serum concentrations, BDNF Val66Met polymorphism and personality profile in drug-naïve schizophrenic patients with first-episode psychosis (FEP) and healthy participants.

MAIN METHODS

This cross-sectional study included fifty FEP patients and fifty healthy participants who served as controls. To study their personality profile the standardized Greek version of the Alternative Five-Factor Zuckerman-Kuhlman Personality Questionnaire (ZKPQ) was administered. Serum BDNF levels were measured and genotyping of BDNF Val66Met polymorphism was performed in patients and healthy subjects.

KEY FINDINGS

FEP patients presented lower BDNF serum concentrations (P=0.002) and higher scores in ZKPQ Neuroticism (P=0.001) and Aggression-Hostility (P=0.002) scales while lower scores in the ZKPQ Sociability scale (P<0.001) than healthy participants. Multivariate analysis revealed that the odds of being assessed with FEP were 0.4 times lower in those with higher BDNF values (P<0.001) and 1.8 times greater in those with higher Neuroticism scores (P<0.001). There were no significant differences with respect to the Val66Met polymorphism between patients and healthy participants.

SIGNIFICANCE

Reduced BDNF serum concentrations along with higher Neuroticism scores might be associated with FEP. A complex interplay between BDNF serum concentrations, personality traits, BDNF Val66Met polymorphism, and psychotic symptomatology has been arisen but further investigation is needed to better clarify the observed associations.

Can genetics inform the management of cognitive deficits in schizophrenia?

There is no doubt that schizophrenia has a significant genetic component and a number of candidate genes have been identified for this debilitating disorder. Of note, several of these are implicated in cognition. Cognitive deficits constitute core symptoms of schizophrenia, and while current antipsychotic treatment strategies aim to help psychosis-related symptomatology, the cognitive symptom domain is largely inadequately treated. A number of other pharmacological approaches (e.g. using drugs that target specific neurotransmitter systems) have also been attempted for the amelioration of cognitive deficits in this population; however, these too have had limited success so far. Psychological interventions appear promising, though there has been speculation regarding whether or not these produce long-term functional improvements. Pharmacogenetic studies of the cognitive effects of currently available antipsychotics, although in relatively early stages, suggest that the treatment of cognitive deficits in schizophrenia may be advanced by focusing on genetic variants associated with specific cognitive dysfunctions in the general population and using this to match the most relevant pharmacological and/or psychological interventions with the genetic and cognitive profiles of the target population. Such a strategy would encourage bottom-up advances in drug development and provide a platform for individualised treatment of cognitive deficits in schizophrenia.